Furnace contkol system



May 24, 1938.

A. MACcHx FURNACE CONTROL SYSTEM Filed April 5, 193e Figi 32.

Inventor:

AMO Macchh Hl Attorney Patented -May 24, 1938 FURNACE CONTROL SYSTEMAldo Macchi, Belleville, N. J., assignor to General Electric Company, acorporation of New York Application April 3, 1936, Serial No. 72,583

1 Claim.

My invention relates to furnace control systems and more particularly tocontrol of furnaces of the type utilizing solid fuel and a forced orinduced draft.

The primary object of my invention is the provision of a new andimproved furnace control having means for automatically feeding the fuelto maintain a predetermined fuel level above the furnace grateandeliminating ashes to maintain a predetermined ash level above thefurnace grate combined with an automatic control of the draft to obtainan even regulation of combustion and providing adequate protectionagainst operating hazards.

In furnaces of the type mentioned diiculties have been experiencedbecause of the fact that the grate bars are likely 4to be deleteriouslyaf- .fected or even melted when subjected to high temperaturesoccasioned by excessive lowering of the ash level and an artificialdraft and, accordingly, it is an object of my invention to provide meansfor preventing the occurrence of such extreme temperatures that wouldmelt the grate.

In carrying out my invention I provide a device responsive to the levelof fuel within the furnace to control the feeding of fuel thereto and adevice responsive to the ashline or grate temperature for controllingthe removal of ashes from the grates of the combustion chamber. A secondthermostat is placed in the room or space to which heat is supplied andit is arranged to control the operation of a draft producing motor inresponse to variations in room temperature. The fuel level responsivedevice and ashline or grate thermostat thus maintain a constantly`burning re, under predetermined normal basic conditions of fuel leveland ash level on the grates within the combustion chamber and whenadditional heat is required the blower lis energized to increase theintensity of the hre.

On the occurrence of high temperatures occasioned by lowering of the ashlevel, the ashline thermostat is adapted to stop removal of ashes fromthe furnace. This usually is suiiicient to reduce the temperature at thenormal ash level to a nominal value but not under cer- -tain conditions,as when the fire is being started or when excessive demands are made onthe 'furnace To safeguard the grate bars under these conditions Iprovide an additional switch in the blower motor circuit that is adaptedto he opened by the ashline or grate thermostat on the occurrence oftemperatures at the norfuel mal ash level above a certain predetermineddangerous value.

Accordingly, it is an object of my invention to provide means controlledby the ashline thermostat of thefurnace for controlling the removal 5 ofashes from the grates of the combustion chamber and preventing operationof the draft producing means when the ashline falls so low that thegrate temperature becomes excessive.

My invention will be better understood from the following descriptionwhen considered in connection with the accompanying.y drawing and itsscope will be pointed out in the appended claim. In the drawing, Fig. 1discloses a schematic diagram of my improved 1l; furnace control; Fig. 2illustrates a modified form of a fuel level responsive device forcontrolling the feeding of fuel to the furnace; and Fig. 3 is amodification of Fig. l showing the ashline or gratethermostat'positioned to be re- 2o sponsive to the grate temperature.

In Fig. 1 of the drawing, I have illustrated my improved control systemin connection with a furnace Il that may be'of any well-known type.Since my invention is not restricted to any type of furnace, the latterhas not been disclosed in detail but it will be obvious to those skilledin the art that any desirable furnace structure may be used. The furnaceis provided with the usual combustion chamber into which fuel is fed ina manner hereinafter to be described. The fuel is indicated, byreference numeral I2 and is fed into the furnace through a conduit I3provided with a screw type conveyer I4. Fuel of the solid type is fedinto the furnace from a hopper I5 from which it is carried upwardly bythe screw conveyer. The coal is conveyed to the apex i6 of the conduitand from there it falls into the combustion chamber past a pivoted fuelgate l1 arranged in the conduit. 4@

Thescrew conveyer` it is driven by any suitable motive means such as anelectric motor It. The motor'is connected by means of rotatable shaft i9to a second screw conveyer 20, the function of which is to remove ashesfrom Within an ash pit 2l.

To support the ash bed and the superposed bed within the combustionchamber there is provided a rotary grate 22 suitably mounted within thefurnace structure. The grate is ro- 5c tated to remove ashes therefromby a pair ol pinion gears 23 driven through a second pair of gears 24,one of which is rotated by any suitable means such as an electric motor25. Gears may be protected from the hot ashes by a slciield-k t5 ingmember 28 adapted to intercept any ashes that might fall upon them.

The combustion chamber is provided with an artificial draft by means ofa blower driven by an electric motor 21, the blower being suitablyconnected to the combustion chamber through a conduit 28. My inventionis applicable equally well to systems utilizing either a forced orinduced draft, and so the apparatus illustrated may be considered asbeing either type.

Before describing the operation of the furnace a brief. detaileddescription of the control will be given. The level of the fuel bedwithin the combustion chamber is maintained at a predetermined value bysuitable control means comprising a light source 28 connected to asuitable source of alternating current supply and adapted to emit lightof a frequency different from the frequency of light emanating from thecombustion chamber. The light emitted from this source is adapted toeffect the operation of a circuit controlling device 3|| in the mannerdisclosed in Letters Patent No. 1,971,191 granted to Harold W. Lord andassigned to the assignee of the present application. The circuitcontrolling device consists of a photo-electric cell and a vacuum tubedevice, adapted to conduct during half cycles of the alternatingcurrent, determining the frequency of the light source and means, suchas a shutter interposed between the two, permitting only light of thepredetermined frequency to affect the photo-electric cell. When a steadylight is thrown upon the photo-electric cell of the device 38 the devicewill not operate to close its associated circuit. It is sensitive onlyto light impulses which are synchronous with the alternating current andwhich have the proper phase relationship with respect to the half wavesthereof. The control is so arranged that when the level of the fuelwithin the combustion cham-V ber is high enough to intercept the beam oflight as indicated in Fig. 1, the control device 30 will de-energize thefeed motor |8 and when the fuel level is below the level indicated thenmotor I8 will be energized. Motor |8 is supplied with power from asuitable source 3| through a manually operated switch 32 and conductors33, 34, and 35. While I have chosen to illustrate the above type of fuellevel controlling device in Fig. 1, any other type may be used and analternative control device is illustrated in Fig. 2. 'Ihe deviceillustrated in the latter figure will be described later.

The ashes Lare removed from the grates of the combustion chamber bymeans controlled by an ashline or grate thermostat indicated at 38. InFig. 3 I have illustrated the thermomat placed in a hollow grate bardriving shaft 22. It is obvious that it may be positioned in eitherplace because of the fact that under normal basic operating conditionsthe ashline temperature bears a certain ratio to the temperature of thegrate bars. 'I'he thermostat may be made, in the customary manner, ofmaterials having dii'ierent coeilicients of expansion and it is adaptedto control the position of a movable contact member 38, moving thelatter to the left on an increase in temperature and to the right on adecrease in temperature. The thermostat controls the energization oi'the grate operating motor 28 through a circuit consisting of conductor31, contact member 38, and conductors 38, 4l, and 4|. It may be seenfrom the drawing that conductors 38 and 4| are connected directly acrossthe power supply lines 33 and 34.

Associated with the ashline thermostat, as the thermostat 38 will becalled hereafter, isa movable contact carrying member 42 adapted to beopened upon a predetermined movement of movable contact 38 when thelatter engages a projection 43 affixed to the former. The stationarycontact associated with movable contact carrying member 42 is connectedto the one side of the source offpower through an electrical conductor44 and the previously mentioned conductor 4|. Movable member 42 itselfis connected to one terminal of the blower motor through an electricalconductor 45. The other terminal of the blower motor y'is connected to aroom thermostat 41 comprising a thermal responsive element 48 and anassociated fixed contact. The latter is connected to the other side of asource of, power through an electrical connection 49.

A description of the `operation of the arrangement just described willnow be given. When it is desired to place the system into operationmanual switch 32 is first closed to connect conductors 33 and 34 to thesource of power 3|. Whenever the fuel level within the combustionchamber falls below a predetermined level, the light Vfrom source 29will render the control device 38 effective to energize feed motor I8through a circuit which is as follows: conductor 33, motor I8, conductor35, control device 38 in circuit closing position, and conductor 34. Itwill be noted that the arrangement is such that the feeding of coal iscontrolled only by the fuel level responsive device. Consequently, thelevel of fuel within the furnace will be maintained at a constant valueunder all operating conditions.

The removal of ashes is in turn controlled by the ashline thermostat 38which controls the grate operating motor 25 to maintain a predeterminedash level within the combustion chamber.. Thus, if the level of ashesrises and effects a reduction in temperature at the normal ashline,thermostat 38 will move to the right and actuate movable contact 38 intoengagement with its associated stationary contact, as illustrated inFig. 1, thereby energizing motor 25. The grate is rotated by the motoruntil the level of ashes within the combustion chamber falls to a pointwhere the temperature at the normal ashline increases to such a valuethat thermostat 38 operates its movable contact 38 to the left asuilicient extent to disengage the contacts. Upon disengagement of thecontacts the motor 28 is deenergized.

From the above it will be seen that I have provided means formaintaining a constant level of fuel within the combustion chamber aswell as means for maintaining a constant level of ashes within thecombustion chamber. This arrangement provides what may be termed a basicfuel bed and ash bed condition that is maintained when no heat is calledfor by the room thermostat. Whenever the thermostat within the room orspace being heated does call for heat then the heating rate is increasedby operation of the blower. On a call for heat by thermostat 41 blowermotor 21 is energized from conductors 33 and ,34 through a circuit whichis as follows: conductors 4| and 44, movable contact carrying member 42in the position indicated i wherein it is in engagement with itsassociated fixed contact, conductor 48, motor 21, conductor 48,thermostatic element 48 in engagement with its stationary contact andconductor 48. In this manneradraftiscreatedintheoombultion nation ofoperation of the grate operating motor is, not enough to prevent theoccurrence of temperatures sufficiently high to damage the tgrate bars.Such conditions occur under unusual conditions that may result when thefire is being started or in response to unusually heavy de- Y mands onthe furnace.

Upon the occurrence ofk high temperatures at the normal ashline theashline thermostat will rst ycle-energize the grate operating motor. Ifthe temperature at the normal ashline rises to a still higher value,movable contact member 38 will be moved further to the left and toengage projection 43 and effect disengagement of the contact carried bymember 42 from its associated iixed contact to de-energize the blowermotor. Thus, the latter cannot be operated again until the temperatureat the normal ashline falls to a safe value.

It may be that under some conditions the temperature obtaining at thenormal ashline within the combustion chamber is of such value that itwould not be desirable to initiate operation of the blower. It will beseen from the drawing and above description that if an excessive ashlinetemperature obtains operation of the blower motor will be prevented.This results from the fact that under these conditions the motorenergizing circuit will b broken by switch 42.

In Fig. 2 I have disclosed a modified form of control for obtainingintermittent feeding to the furnace to maintain a predetermined level offuel in the combustion chamber. In this modiilcation I have provided anelectrical motor I8 adapted to drive the screw conveyer |4 through achange-speed device 5|. Motor I8 is supplied with energy from the source3| through electrical conductors 33. 34, and 35. The circuit betweenconductors .34 and 35 is adapted to be closed when the level of fuelwithin the combustion chamber falls below a predetermined value.

In this modification I have shown mechanical means, indicated generallyat 52. for closing this circuit. The mechanical means 52 thus takes theplace of the light source 29 and the light responsive circuitcontrolling device illustrated in Fig. l. Through the medium of thechange-speed device 5| I drive a pinion gear 53 adapted in turn to drivea second pinion gear 54. 'Ihe latter drives the shaft 55 to which areaflixed a conducting circuit controller 56, provided with an insulatedportion 51, and a cam 58. The conducting portion of the circuitcontroller is connected to conductor through a conductor 55 and a secondconductor 60 is connected to a contact brush 6| adapted to ride on theouter periphery of the circuit controller. The cam 58 co-operates with acam follower 62 co-operating 10 with a pivoted contact carrying arm 63,suitably pivoted at 64. The latter member is connected by a rod 65 to asecond pivoted lever 66 whose position is controlled part of the time bythe level of the fuel within the furnace. 'Ihe latter member is suitablypivoted as at 66'.

In operation, when the level of the fuel falls to a predetermined valuearm 66 moves in a clockwise direction, causing movement of pivoted arm63 in a counter-clockwise direction and engagement of contacts 61 and68. Engagement of these contacts energizes motor i8 through a circuitthat is as follows: conductor 33, motor IB,

conductor 35, contacts 61 and 68 in their closed position, and conductor34. Energization of motor I8 in turn effects rotation of screw I4 forfeeding fuel to the furnace. Simultaneously, pinion 53 is rotatedthrough the change-speed device 5|, effecting in turn rotation of pinion54 and shaft 55 in a clockwise direction. Rotation of shaft 55 effectsrotation of circuit controller 55 and cam 58. Rotation of the circuitcontroller closes a shunt circuit across contacts 61 and 68 throughconductors 59, 60, contact brush 6|, and the conducting portion ofcircuit controller 56.

Motor I8 thus is maintained energized until the circuit controller 56 isrotated to the position indicated in Fig. 2 wherein the circuit isbroken by engagement of contact brush 6| with insulated portion 51. Therotation of shaft 55 through 360 also rotates cam 58- and moves thefloating arm 66 counter-clockwise so that it will be out of contact withthe coal during the feeding period.

The length of the feeding period may be adjusted so that motor I8 willoperate through several cycles before the level of coal within thecombustion chamber is raised sufficiently to prevent contacts 61 and 68from engaging each other. This is 'accomplished by adjustment of thechange-speed device 5| to vary the speed of rotation of gear 53. On theother hand, the rate of fuel feeding may be chosen so that it will benecessary to go, through the above described cycle but once to raise thelevel of coal to the desired value.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

The combination of a furnace having an operable grate supporting an ashbed and a superposed fuel bed in which the consumption of fuel resultsin variation in the relative height of the ash bed and fuel bed, meansfor operating the grate to decrease the height of said ash bff. meansfor supplying fuel tosaid furnace to increase the height of said fuelbed, means fr supplying said furnace with combustion air to control theconsumption of fuel, means responsive to the fuel level Within saidfurnace for controlling said fuel feeding means, thermal responsivemeans located in the space heated by the funace for selectivelycontrolling the operation of said combustion air supply means inaccordance with variations in the space temperature, and thermostatiomeans responsive to a temperature dependent upon the height of said ashbed above said grate for selectively controlling the operation of saidgrate operating means upon variation of said temperature betweenpredetermined values and having a separately operable control means forpreventing operation of said air supply means when said temperatureexceedsI a predetermined higher value.

ALDO MACCHI.

